For low-frequency currents(up to about 15, 000 cycles per second)an iron core, called a magnetic circuit; is placed.是什么意思_For low-frequency currents(up to about 15, 000 cycles per second)an iron core, called a magnetic circuit; is placed.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句